Based on the aperture coupled method, a metal-insulator-metal voltage tunable filter is proposed. The filter consists of two asymmetric rectangular ring resonance cavities and a rectangular waveguide, in which the asymmetric rectangular ring cavity is filled with organic electro-optic material 4-dimethylamino-N-methyl-4-stilbazolium tosylate. Finite element numerical simulation method is used to calculate and analyze the transmission spectrum, resonance wavelength distribution curve, and magnetic field intensity distribution of the asymmetric rectangular ring cavity waveguide structure. The results show that the filter has smooth transmission spectra, wide passband bandwidth with transmittance as high as 97%, and wide stopband bandwidth with transmittance as low as 0.01%. The characteristics of the filter can be adjusted not only by changing the structural parameters, but also by applying a control voltage. The adjustability of the filter is higher, and the proposed optimized structure has a wider stopband. Therefore, this type of filter can be well applied in integrated optics.